Image forming apparatuses are devised to form an image on a printing medium. Examples of image forming apparatuses may include, e.g., printers, copiers, facsimiles, and so-called multi-functional devices that combine some of the functionalities of the aforementioned devices.
In an electro-photographic image forming apparatus, which is one type of image forming apparatuses, the surface of a photoconductor pre-charged to a certain electrical potential is exposed to light so as to form an electrostatic latent image thereon, which latent image is then developed into a visible image by means of a developer feed device that applies the developer to the electrostatic latent image. So formed visible image is then, transferred from the photoconductor to a printing medium either directly or indirectly by way of an intermediate transfer unit. Such image forming apparatus typically also include a charge eliminating unit for eliminating the residual electric potential remaining on the surface of the photoconductor after the transfer of the visible image and before charging of the photoconductor to begin the next image forming operation.
Generally, a charge eliminating unit includes a light source and a light guide that guides the light generated from the light source to the photoconductor. The configuration of the light guide affects the charge elimination performance. That is, to achieve a uniform charge elimination along the length of the photoconductor, the light emission from the light guide also needs to be sufficiently uniform along the same length direction of the photoconductor. In addition, for an effective charge elimination, a sufficient amount of the light received from the light source need to be delivered by the light guide to the photoconductor, which means the light emission face of the light guide needs to have a sufficiently low loss of light.
In addition to its use in a charge eliminating unit of an image forming apparatus, a light guide may also be found in a light source unit of an image reading apparatus for guiding light from a light source across a document being read. In such image reading applications, too, the afore-mentioned low light loss and uniform light emission characteristics of a light guide is desirable.